Commitments and Contingencies (Details Textual) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jul. 31, 2012	Jul. 31, 2011
Corporate Headquarters [Member]
Lease Expiration Date	Apr. 30, 2014
Operating Leases, Rent Expense	$ 17,000
Laboratories and Office Space [Member]
Lease Expiration Date	Jun. 30, 2014
Operating Leases, Rent Expense	16,000	13,000
Office Headquarters [Member]
Lease Expiration Date	Jul. 31, 2013
Operating Leases, Rent Expense	$ 7,000	$ 7,000